For many decades, UV radiators have been used for disinfecting drinking water and waste water in air conditioning sumps and for disinfecting working areas in biological laboratories.
In UV water treatment plants, UV-C radiation sources are arranged in a silica glass sleeve tube in order to irradiate the water. The sleeve tube protects the radiation source from external damage and simultaneously ensures an efficient operating temperature.
UV disinfection plants generally comprise a plurality of UV radiators which are arranged in a throughflow reactor, through which water flows, or in an open channel. While flowing through the reactor or the channel, the water is exposed to an adequate dose of UV-C radiation so that the desired effect is achieved. To monitor the dose released into the water, a UV sensor is conventionally provided in the reactor, which is arranged orthogonally to and at a distance from the radiator surfaces and which receives a signal which is representative of the radiant power released into the water. This measurement can also detect a change in the irradiation intensity, but it cannot detect the cause thereof. The irradiation intensity detected by a UV sensor is influenced by many factors, such as aging of the UV radiator or of the UV sensor, a coating formation on one of the silica sleeve tubes surrounding the UV radiator and a change in the quality of the water.
In this respect, the water quality is of particular interest, because the ideal dose of UV depends thereon, inter alia. The UV radiation is weakened by substances which are dissolved in the water. In particular, iron, manganese, humic acids and other organic ingredients have an influence on the UV transmittance. Therefore, the UV transmittance must be measured in order to determine the water quality. The weakening of the UV radiation by the water is heavily dependent on the wavelength. Therefore, the UV transmittance is determined using the wavelength of 254 nm which is effective for the UV disinfection of water. A separate transmission measurement method is conventionally used to measure the UV transmittance.
U.S. Pat. No. 6,791,092 B2 discloses, for example, a transmission measuring device which has an analysis chamber for the passage of a liquid, in which a UV radiator and three UV sensors, attached at different intervals from the UV radiator, are arranged. By evaluating the measurement signals, it is possible to infer the transmittance of the liquid via the shape of the arrangement.
Typical values of the UV transmittance are 85-98%/cm for drinking water and 50-75%/cm for waste water.